NGT—Checks and adjustments
190 NGT Transceiver System Technical Service Manual
Checking performance of the receiver
Checking the sensitivity and (signal+noise)/noise ratio
To check the sensitivity and (S+N)/N ratio:
1 Connect an AC voltmeter across the audio output (loudspeaker).
1 Press 5 to select RF Gain On.
1 Connect the signal generator to the RF connector ( ).
1 Select any channel.
1 Set the frequency of the signal generator 1 kHz above the suppressed carrier
frequency of the selected channel (1 kHz below for LSB).
1 Set the signal generator output level to –121 dBm (0.2 mV PD).
1 Adjust the volume control for a suitable, near full-scale dB reading on the AC
voltmeter.
1 Record the reading.
1 Switch off or adjust the output of the signal generator to a frequency outside the
receiver pass-band.
1 Check that the audio output drops by at least 10 dB.
1 Repeat the above with the RF gain off and the output of the signal generator set to
–103 dBm (1.5 mV PD).
1 Check that the audio output drops by at least 10 dB.
If the audio output does not drop by at least 10 dB, further analysis is required.
NOTE
The transceiver does not have to be in Service mode to perform any of the
checks in this section.
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